CMR Protocol: An IV injection into the antecubital vein and connected to a power injector will be performed in the MR scanner for functional and perfusion imaging (Symphony 1.5 T, Siemens Medical). All images are acquired with a 4 channel phased array surface coil. Blood flow imaging is performed in three short-axis simultaneous slices (basal, mid and apical) acquired during an initial bolus injection of gadolinium (0.04 mmol/kg at a rate of 5 ml/sec) followed by a 10-ml saline flush administered using the power injector. ProHance is used due to its lower viscosity as the contrast agent. The short-axis slices are acquired using a SSFP imaging sequence with, TR/TE/flip 185ms/1.2ms/50 degrees dynamically acquired and inserted into a 330x 380 matrix). Images are acquired using a field of view ranging from 280 to 400 mm. A first perfusion scan will be performed at rest, followed by a second scan during maximal vasodilation about 15 min later. Hyperemia will be initiated with administration of 400 mcg bolus injection of regadenoson and acquisition started 1 minute post regadenoson administration. Subjects will be monitored using MRI compatible blood pressure monitoring and single lead ECG monitoring.